1. Field of the Invention
The present invention relates to network devices, and more particularly, to a technique of providing power to a network device.
2. Description of the Prior Art
Power over Ethernet (POE) is a technique that can be utilized to supply power to a network device through communication cable(s) of an Ethernet network. By utilizing this technique, the network device can obtain power required for operation through the communication cable(s) of the Ethernet network.
FIG. 1 shows a schematic diagram illustrating a Power over Ethernet (POE) system. A network 100 shown in FIG. 1 includes a first network device 110 and a second network device 120, both of which being capable of supporting the POE technique. More specifically, in this example the first network device 110 is a device for providing power, while the second network device 120 is a device being provided with power. For example, the first network device 110 is a switch and the second network device 120 is an end station.
The first network device 110 includes a power supplier (not shown), a transmitter 112 and a receiver 114. The second network device 120 includes a transmitter 124, a receiver 122, and a relay 126 shown in FIG. 1. The relay 126 is coupled to a first receiving end VIP, a second receiving end VIN, a first transmitting end VOP, and a second transmitting end VON of the second network device 120.
When required operational power is not yet provided to the second network device 120, the two switches in the relay 126 should be in “ON” states to let the first receiving ends VIP and VIN be interconnected with the first transmitting ends VOP and VON, respectively. Under these circumstances, a link pulse sent by the transmitter 112 will be returned to the receiver 114 (the link pulse returned to the receiver 114 is attenuated). If the first network device 110 receives the returned link pulse, according to the specification of the POE, the first network device 110 realizes that the second network device 120 supports the POE technique. The first network device 110 can then send power to the second network device 120 through the communication cables connected between the first network device 110 and the second network device 120. When the required operational power is already provided to the second network device 120, the two switches in the relay 126 should be in “OFF” states.
The block “relay 126” shown in FIG. 1 is only a conceptual block. The detailed circuit structure is more complicated than what is shown in FIG. 1, which includes only two switches. It is required to appropriately design the relay 126 utilized in the second network device 120 to let the POE function be properly carried out. Besides, it is also required to integrate the relay 126 in a chip to reduce the overall manufacturing cost.